It has been a while since I mentioned any Unity 3D tutorials on this site, as I only wanted to mention those that I felt were particularly relevant for iOS developers.

Rocket 5 Studios has created an excellent series of guides on developing 2D games with Unity 3D that together make for an excellent tutorial. There are many ways to create 2D games with a 3D game engine such as Unity, and these tutorials explain how to do so using 2D sprites and also explain how to use 3D models as the background within your 2D games.